Non-reciprocal devices, in which time reversal symmetry is broken for light propagation, provide functionalities for signal routing and source protection in photonic systems. Commonly encountered nonreciprocal devices include isolators and circulators, which can be implemented using a variety of techniques encompassing magneto-optics, parity-time symmetry breaking, spin-polarized atom-photon interactions, and optomechanical interactions. Recent development include using time-reversal symmetry breaking for imparting protection against defects, through analogues of the quantum Hall effect in both topological and non-topological systems.
While the present invention is susceptible to various modifications and alternative forms, exemplary embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description of exemplary embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the embodiments above and the claims below. Reference should therefore be made to the embodiments above and claims below for interpreting the scope of the invention.
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